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Biomedical subjects

S T Chandler

Publications and source records attributed to S T Chandler.

At least 19 recordsLinked to original sources
PubMed1998

A new method for measuring aerosol nebulizer output using radioactive tracers.

Reproducibility and comparability of bronchial challenge tests depends critically on accurate assessment of nebulizer output. Evaporation during nebulization means that simple weighing is inaccurate, overestimating the delivered dose of active ingredient. We wanted to quantify this effect in the context of intermittent nebulization, using a dosimeter as used in bronchial provocation tests. Output of three types of nebulizer, from the MEFAR dosimeter, was measured by radioactive tracer, using a standard solution of technetium-99m-pertechnetate (1.5 kBq x mL(-1)) in 4 mL of normal saline. The aerosol was impacted by suction onto a microfilter, and the radioactivity measured. Nebulizers were weighed before and after nebulization. Ratio of nebulized volume calculated from the radioactivity on the filter, to the total volume loss by weight, was expressed as nebulized ratio. The effect on output of two concentrations of methacholine, two tracers of different weights, and change in temperature, were assessed. Nebulized ratio varied between 44.1-71.6%. Results were more consistent within the same type of nebulizer than between different makes. Neither changes in molar concentration nor molecular weight affected nebulizer output or nebulized ratio. Mean nebulized ratio was 58.5%, showing that calibration by weighing, overestimates the delivered dose by a factor of approximately two. Measuring radioactivity eluted from a microfilter, onto which nebulized output had been impacted proved to be a satisfactory method of calibration.

Aerosols↗
PubMed1994

Is respiratory sinus arrhythmia present in atrial fibrillation? A study using two quantitative methods.

Two quantitative techniques have been evaluated to examine whether respiratory sinus arrhythmia can be detected in atrial fibrillation. Cyclical changes in heart rate during deep breathing indicating respiratory sinus arrhythmia were seen in 11/15 control patients, but only 1/44 patients with atrial fibrillation. Power spectrum analysis suggested that more subtle variations in heart rate with breathing may be present in some patients with atrial fibrillation where it was not detectable by simpler techniques. These results support the hypothesis that although respiratory sinus arrhythmia is not detectable in atrial fibrillation by conventional means, there may still be some mediation of heart rate either by vagal or extravagal mechanisms.

Aged↗
PubMed1990

Uptake of radioiodinated cardiac specific troponin-I antibodies in myocardial infarction.

STUDY OBJECTIVE: To examine the potential diagnostic value of the cardiac myofibrillar protein troponin-I as a target for radiolabelled antibodies in detecting heart damage, the uptake of 131I labelled polyclonal cardiac troponin-I Fab was investigated in necrotic myocardial cells in canine myocardial infarction. DESIGN: Cardiac specific troponin-I Fab was prepared by immunoaffinity chromatography and injected 5 h after coronary artery ligation. Whole body gamma camera scintigraphic images were taken after the injection, and heart slices were examined for the presence of labelled antibody. SUBJECTS: Adult dogs of either sex (n = 6) were used. MEASUREMENTS AND MAIN RESULTS: Scintigraphic whole body images at 24 and 40 h after troponin-I Fab injection showed increased 131I-localisation over the apical region of the heart which corresponded to the infarcted areas. Localisation in infarcted tissue was confirmed in isolated heart and histochemically stained heart slice images. Uptake of 131I Fab was up to 24 times greater in necrotic than in normal myocardium and was inversely related to regional blood flow as determined by 141cerium microsphere distribution. Confirmation that 131I Fab uptake was due to direct binding to troponin-I in necrotic cells was obtained by coinjection of non-immune 125I labelled Fab. CONCLUSIONS: Results indicate that troponin-I could act as a suitable target for detecting myocardial necrosis.

Animals↗
PubMed1990

Models of renal blood flow and their use in the detection of renal artery stenosis.

First-pass studies of renal blood flow using 99Tcm-DTPA have been analysed in normotensive patients and those with renal artery stenosis. One and two component models of renal blood flow were examined for their ability to discriminate between these two groups. Using a two component model, 5/7 kidneys with proven renal artery stenosis were identified, with 38/40 kidneys in normotensive patients lying within the defined normal range. The two kidneys not detected by this technique both had extremely poor function. This model was also applied to other hypertensive patients referred for routine screening and appears promising in increasing the specificity of the 99Tcm-DTPA study for detecting renal artery stenosis.

Adolescent↗
PubMed1989

A comparison of liver-spleen ratios and uptakes obtained using planar and tomographic techniques.

Liver-spleen ratio, volume and uptake were measured in 20 patients undergoing routine 99Tcm-colloid examinations. Methods using planar views only were compared with results obtained using SPECT techniques and automated slice processing. The results suggest that a reasonable estimate of liver-spleen ratio may be obtained using anterior and posterior planar views only. Estimates of organ volume and absolute uptake were not reliably obtained using planar views only, and SPECT studies are required. The choice of attenuation correction technique for SPECT studies did not affect the results obtained for liver-spleen ratios and volumes, although systematic underestimation of absolute uptake occurred with simpler techniques.

Adult↗
PubMed1987

Splenic platelet-sequestration following routine blood transfusion is reduced by filtered/washed blood products.

The mean fall in the platelet count following 23 routine transfusions of 3-5 units packed cells for anaemia was 32.5%. This was significantly reduced to 12.5% in 15 similar transfusions through a 40 microns microaggregate filter (P less than 0.01) and to 4.6% following five transfusions through a polyester fibre filter (P less than 0.005). In 10 transfusions with frozen or polyester fibre filtered, washed red cells, the decrease in platelet count was 4.2% (P less than 0.001). A study of 111In-oxine labelled autologous platelets in nine patients indicated that the fall in platelet count was due to increased splenic sequestration. Since thrombocytopenia following routine transfusion is reduced by procedures which filter the packed cells, the decrease in platelets is probably caused by their adherence to infused microaggregate debris causing their premature removal from the circulation. Patients with preexisting thrombocytopenia who receive red cell transfusions for anaemia, should therefore receive blood products depleted of microaggregate debris in order to avoid exacerbation of thrombocytopenia and haemorrhagic complications.

Anemia↗
PubMed1987

An evaluation of anti-insulin radioimmunodetection in patients with suspected insulinoma.

Nine patients with suspected insulinoma were scanned with iodine-131 labelled anti-insulin. The clinical diagnosis was subsequently confirmed at laparotomy in eight patients, two of whom had liver metastases. The primary insulinoma was accurately localized by anti-insulin scanning in four patients and these tumours ranged from 1 to 3 cm in diameter. Both computerized axial tomography (CT) scanning and pancreatic angiography had given false negative results in one of these patients. Hepatic metastases were correctly identified in one of two patients. No hepatic false positive reports occurred. Positive scan areas were graded as definite, probable or possible. All four of the pancreatic positive results graded as definite or probable positive were correct. Three false positive results occurred in the region of the pancreatic body, all had been graded as possible. Anti-insulin scanning failed to detect four subsequently proven insulinomata (3 mm-2 cm in diameter). Pelvic uptake of anti-insulin occurred in a patient who was found to have a para-ovarian tumour. An homogenate of this tumour also reacted with anti-insulin in a radioimmunoassay. A true negative pancreatic scan was obtained in this patient. We conclude that this technique is insufficiently accurate for routine clinical use.

Adenoma, Islet Cell↗
PubMed1987

A method for thresholding subtracted images in radiolabelled-antibody imaging.

The low target-to-background ratio of radiolabelled antibodies often necessitates the use of a subtraction technique to enhance areas of tumour uptake. However, interpretation of the results is often difficult due to noise in the antibody and subtraction images. By performing a linear, least-squares fit to all the pixel values, it is possible to calculate the "prediction interval". This may be used as a variable threshold for the subtracted image to leave only statistically significant counts. The method has been evaluated in models and found to be independent of count density and image processing. Useful results have been obtained in initial patient studies. The technique is fast and objective, and therefore it may have a useful role in the routine analysis of subtracted images.

Antibodies, Monoclonal↗
PubMed1986

Clinical evaluation of anti-alpha-fetoprotein radioimmunodetection.

Anti-alpha-fetoprotein (AFP) radioimmunodetection was performed in response to clinical requests in 16 patients. In two patients, assessment of a known tumour was required; the anti-AFP scans were accurate and provided useful clinical information in both cases. In the remaining 14 patients the request was for localisation of suspected recurrent tumour. Accurate information was provided in four of these patients. In this latter group, various conventional methods of investigation had failed to disclose the site of recurrence. However, of a total of 21 sites reported as positive in these 14 patients, eight proved to be false positives. Two false negative results also occurred in this group and nine could not be evaluated. Although occasionally patients were usefully scanned, improvements are necessary before consistently reliable information can be obtained using this technique.

Abdominal Neoplasms↗
PubMed1985

111-Indium platelets in monitoring pancreatic allografts in man.

A technique for monitoring pancreatic allografts in man is presented. The method utilizes 111-indium labelled autologous platelets and provides quantitative and qualitative analysis of uptake of the tracer by the graft. Five patients without any significant accumulation of radiolabelled platelets in their transplants had an uneventful recovery and left hospital with satisfactory graft function. The three patients who suffered graft failure showed abnormal uptake of the tracer. This presented as a diffuse platelet accumulation within the transplanted pancreas in the case of acute rejection, or as a focal accumulation in two cases of venous thrombosis. Minor complications such as perigraft haematoma can also be diagnosed using this technique. We suggest that 111-indium labelled platelets provide a valuable diagnostic aid in the management of pancreatic transplant recipients.

Adolescent↗
PubMed1985

The effect of gastric partitioning on gastric emptying in morbidly obese patients.

Gastric partitioning is undertaken for morbid obesity but the mechanism by which weight loss is achieved is unclear. The effect of partitioning on gastric emptying has therefore been studied. In thirty patients with a mean weight of 124.6 +/- 7.3 kg (+/- s.e.m.), a stapling technique was used to create a 50 cm3 upper gastric reservoir which communicated via a 10 mm stoma with the distal stomach. Twenty-four pre-operative and nineteen postoperative gastric emptying studies were performed using separate 50 cm3 solid and liquid 113m In-labelled meals. The time taken to achieve 50 per cent gastric emptying and the delay in isotope reaching the duodenum were measured from gamma camera images. There was no correlation between the pre-operative weight of the patients and their gastric emptying rates. The median 50 per cent gastric emptying time for solids was increased from 21 min (range 8-34) to 37.5 min (range 8-60) (P less than 0.001), unpaired Wilcoxon), but was little changed from 17 min (1.5-30) to 16 (1.5-30) min using liquids. Delay in arrival at the duodenum was increased for solids from 0.5 min (0.5-13) to 2.5 min (0.5-42.5) (P less than 0.05) but again there was no significant effect on liquid emptying. Postoperative 50 per cent emptying time for solids correlated with mean weight loss at 3, 6, 9 and 12 months (P less than 0.05). Following gastric partitioning there is delayed emptying of solids with related weight loss but liquid emptying is unaffected.

Body Weight↗
PubMed1983

Indium-labeled platelet uptake in rejecting renal transplants.

The uptake of 111In autologous platelets in transplanted kidneys was measured in 16 patients shortly after operation. Each patient was then observed for two years. When transplant radioactivity had increased, despite treatment for acute rejection, the kidney was ultimately lost because of rejection.

Adult↗
PubMed1978

The assessment of aorto-iliac disease by static isotope angiology.

In 48 patients with severe claudication isotope images of the aortofemoral arteries have been assessed for the severity of disease in 417 anatomical segments and compared with arteriography. An overall correlation of 80 per cent was found; 87 per cent of patent and 76 per cent of occluded segments were correctly identified, but only 68 and 54 per cent of segments with minor and major disease respectively. Underestimation of disease occurred in only 6 per cent.

Adult↗